${\mathrm{BaCu}}_2{\mathrm{Si}}_2{\mathrm{O}}_7$: A quasi-one-dimensional $S=1/2\mathrm{}$ antiferromagnetic chain system

The antiferromagnetic (AF) compound ${\mathrm{BaCu}}_2{\mathrm{Si}}_2{\mathrm{O}}_7$ is studied by magnetic susceptibility and neutron-scattering techniques. The observed behavior is dominated by the presence of loosely coupled $S=1/2\mathrm{}$ chains with the intrachain AF exchange constant $J_{\Vert }\approx 24.1$ meV. Long-range Néel ordering is observed below $T_N=9.2\mathrm{}$ K. The results are discussed within the framework of the mean-field RPA model for weakly interacting quantum spin chains.